I started to use C2 when it was in early-adopter stage. Since then I tried Unity, GameMaker, Stencyl, but I always came back here. C2 is fast, easy to use, and it has many other positive things to make it a great engine. It has a few permormance issues, but it's not because of C2 would be a poorly written engine, but because the technology is based on. HTML5 performance is greatly affected by the current browsers (even, when you export your game to an .exe file, you wrap your HTML5 game with the Chromium browser). An other very usual cause of the performance issues is bad game design. Yes, it's easy to use, but it doesn't mean you can ingore the optimization of your game, and it's true with all engines. I personally yet to encounter any serious performance problem, but I value the opinion of others who already had.
As it was mentioned before me, C2's event system helps you learn programming. It doesn't help you to get to know an actual language (unless, you're developing a plugin with the SDK in JS), but it helps you with the logic that you can use with any language. The hard part of learning programming is getting to know the logic, developint your algorithmic skills. And C2 is great for that.
You can make almost anything with C2. I say almost, because it's not designed for 3D, but there's the Q3D plugin for that.
Some pros:
- Easy to use GUI
- Powerful event system for visually programming your game
- SDK for writing custom plugins
- Great and rich documentation
- Friendly community and developers
- Great licensing policy (you buy once, get all features, updates and platforms, and you can use your license offline as well)
Some cons:
- It's based on HTML5 and for some people it can be a problem.
- The editor is Windows only (C3 is going to change that in the future).
- No modularity and co-working in the engine (planned for C3).
- Designed for 2D (it also counts as a pro, but if you're looking for 3D, you either have to use the Q3D plugin as mentioned before, or you'll have to go with an other engine).
- Using wrappers for supporting different platforms (like the .exe wrapping example at the beginning of my post).
Overall, I'd highly recommend getting this engine. It's one of the best representatives of the new era of programming a software visually. It's easy and fun to work with and you'll get results pretty fast. You won't regret it. That's my opinion about it